Automobiles that incorporate an electric motor in their drive power source, such as electric automobiles and plug-in hybrid vehicles, have been gaining in popularity in recent years, and the installation of charging stands for charging the batteries in such automobiles is progressing. In addition, charger connectors for electric automobiles for battery charging, as well as holders for battery capacitors, have entered into use.
A high degree of flame retardancy is required of the housings that are a component of charger connectors for electric automobiles, battery capacitor holders, and charging stands for electric automobiles, and a thing made of metal is thus frequently used. In addition, efforts are also being made to convert this to plastics and a variety of resins are under investigation.
Among these resins, polybutylene terephthalate has favorable properties as an engineering plastic, e.g., an excellent heat resistance, moldability, chemical resistance, and electrical insulation performance, and as a consequence is used in, for example, electrical and electronic parts, automotive parts, other electrical parts, mechanical parts, and so forth. Investigations are underway to provide polybutylene terephthalate with flame retardancy.
As a general method for imparting flame retardancy to polybutylene terephthalate, a method for compounding a flame retardant using a halogen compound and antimony trioxide as a flame retardant synergist (refer to Patent Documents 1 and 5 to 8) are well known. Moreover, charger connectors for electric automobiles, battery capacitor holders, battery capacitor housings, and charging stands for electric automobile are—just as with other electrical and electronic parts—undergoing wall thinning and downsizing due to the trend toward smaller and lighter devices, and the moldings used in these applications are thus also undergoing downsizing and wall thinning. While a high degree of flame retardancy is required of these thin-walled moldings, it is increasingly difficult to achieve flame retardancy as the wall of a molding becomes thinner.
Moreover, in addition to flame retardancy, an excellent tracking resistance, which is one of electrical properties, is required in the electrical and electronic equipment field in order to ensure safety with respect to fire induced by electrical load.
With regard to materials that seek to provide an improved tracking resistance, Patent Document 9 discloses a resin composition that contains a thermoplastic polyester resin and an olefin copolymer formed of an α-olefin and the glycidyl ester of an α,β-unsaturated acid, and teaches that an ordinary flame retardant; a filler such as talc, kaolin, silica, and so forth; and a fibrous filler such as a glass fiber may be added on an optional basis. Patent Document 10 teaches a resin composition containing polybutylene terephthalate, brominated polycarbonate flame retardant, antimony flame retardant synergist, ethylene fluoride polymer, polyolefin, and a metal silicate filler and a glass fiber. Patent Document 11 discloses a resin composition containing a thermoplastic polyester resin, densified microfine talc powder, and a halogenated benzyl(meth)acrylate flame retardant, and teaches that a fibrous reinforcing agent may be added on an optional basis.
None of these resin compositions, however, were necessarily able to perform satisfactorily with regard to providing both flame retardancy and a high impact resistance.
In addition, due to its excellent crystalline characteristics, polybutylene terephthalate has the problem of having an unsatisfactory toughness, as represented by the impact strength, and in order to solve this problem research into polymer alloys has been underway for some time; various flame retardant formulations have also been introduced here.
For example, Patent Document 2 discloses a flame retardant polyester resin composition having the following as constituent components: polybutylene terephthalate resin, polycarbonate resin, halogen flame retardant, flame retardant synergist, and transesterification inhibitor. Patent Document 3 discloses a flame retardant polyester resin composition that contains a polybutylene terephthalate resin, polycarbonate resin, elastomer, flame retardant, and flame retardant synergist. In addition, Patent Document 4 discloses a polyester resin composition that contains a polyester resin, polystyrenic rubber, and flame retardant.
However, the properties required in the electrical and electronic equipment field have become increasingly stringent, and, in addition to flame retardancy and impact resistance, heat aging resistance, lightfastness, moist heat resistance, hydrolysis resistance, and a uniform and good quality appearance are also required, but it has been quite difficult for conventional formulations to respond here.
An excellent mold-releasability that avoids an increase in the releasing resistance force is also required in injection molding, and, for example, the following are strongly required: no generation of ejector pin marks during demolding, excellent surface appearance, and absence of warping.
Patent Document 1: Japanese Patent Application Laid-open No. S61-66746
Patent Document 2: Japanese Patent Application Laid-open No. 2007-314664
Patent Document 3: Japanese Patent Application Laid-open No. H6-100713
Patent Document 4: Japanese Patent Application Laid-open No. 2005-112994
Patent Document 5: Japanese Patent Application Laid-open No. 2004-263174
Patent Document 6: Japanese Patent Application Laid-open No. 2006-45544
Patent Document 7: Japanese Patent Application Laid-open No. 2006-56997
Patent Document 8: Japanese Patent Application Laid-open No. 2011-84666
Patent Document 9: Japanese Patent Application Laid-open No. H7-196859
Patent Document 10: Japanese Patent Application Laid-open No. H10-67925
Patent Document 11: Japanese Patent Application Laid-open No. H10-158486